shell: shell to achieve using Linux batch management, rather than developing applications
shell can be associated with a better third-party libraries
1, bash's basic features:
ctrl+l
The key
history
2, IO and redirection pipe character
(1) IO redirection: change the default location
1, > standard output redirection:
ls> / dev / pts / 5 ls command to redirect the output window. 5
ls> /data/ls.out ls command to redirect output to file /data/ls.out
Note: If the file already has the content ls.out then after redirect the output file will overwrite any original content
2 >> : append redirection, the new content will be added to the target end of the file
ls >> /data/ls.out
3, () : standard merged output a plurality of programs
(cal 2007;cal 2008) > all.txt
4, 2> standard error of the output redirection:
2 cmd> /data/err.log cmd (cmd command itself is no, the input command will display an error results) redirect error result to display data / err.log in
Note : history 2> /data/err.log because of their history command is correct, so the default output device will normally display the contents of the command history, and not output to /data/err.log in. Original data / err.log files will be overwritten empty file.
cmd 2 >> /data/err.log This will display the correct information on the default output device, and an error message each time input to err.log file for easy research questions behind
5, < standard input redirection
cat <File File contents of the input file to the cat command
(2) pipe symbol
Pipe (using "|" symbol shown) for connecting the command
command 1 | command 2 | command. 3 | ...
- The standard output of a command sent to the command STDIN 2, 2 standard command output command is sent to the STDIN. 3
- The default forwarding STDERR not pipe, can use 2> & 1 | & implemented
ls /data /err 2>&1 | tr 'a-z' 'A-Z' ls /data /err |& tr 'a-z' 'A-Z'
3, Programming Basics
Principles of Programming
Program: implementation of a code of a function
= Program comprising instructions (commands) + + (logic) Data (variable)
4, grep and regular expressions:
Linux Three Musketeers: grep, sed, awk
patten "mode"
5 logic, statement
Branch:
if
case: * use the startup script writing implement case of Linux *
cycle:
for: Add to the list for the cycle
while: do satisfy the judgment condition cycle is True --- Do not enter an infinite loop
until: satisfies the determination condition do loop is False ---- /
break: out of the loop
continue: to interrupt this cycle, the next cycle continues
exit: Exit the current program, the return value of the specified program
read: Input
echo: Output
Linux Three Musketeers:
sed: stream editor
Switch between the two modes
awk：
The main job of the report generator, is an independent programming language
grep: filter
function:
A fixed function block
Array:
String:
String Processing
Exercise
1, it is determined / etc / inittab file is greater than 100 lines, if yes, display the "/ etc / inittab / is a big file." Otherwise Display "/ etc / inittab is amall file."
#!/bin/bash
#
Line = `wc -l /etc/inittab | cut -d’ ‘ -f1
if [ $Line -gt 100];then
echo “/etc/inittab/ is a big file.”
else
echo“/etc/inittab/ is a smal file.”
be
1, bash's basic features:
a) command to expand:
The date command - Create command based on the date command
date: View the system clock
Check the hardware clock: clock, hwclock often synchronize the system clock with the hardware clock
cal View Calendar
date +% F: change the format of the output date 2019-08-05
date +% F-% H-% M-% S output: = 2019-08-05-14-29-15 years - when - - May - Day minutes - seconds
%F = CCYY-mm-dd
%H = hh
%M = MM
%S = ss
%T = hh:MM:ss
%D = mm/dd/YY
Exercise: Create a log file for a month's statement cycle (2019-08-06.http.log)
# 或者touch `date +%F`.http.log
for i in {1..30};do
touch `date +%Y-%m-$i`.http.log;done
Linux directory rule to follow: FHS directory rules
{}: Extended e.g. cp / etc / inittab /etc/inittab.bak == cp /etc/{etc/inittab,/etc/inittab.bak}
tar: Archive tool - can be operated directory
Compression tools: gzip, bzip2, xz compression can only manipulate files, directories can not operate
zcat view compressed files without decompression
Common parameters of tar:
-j corresponding to the compression tools bzip2
-J the corresponding compression tool xz
-z gzip compression tool correspondence
-c compression
-x decompression can not specify an extraction tool
-f specify the file name
-v Show Details
-C specifies the extracted directory
-t not view the contents of decompression, the same zcat
Examples: tar cjvf 2018-08.http.log.bz2 2018-08 * .http.log compression
tar xvf 2018-08.http.log.bz2 -C / abc / decompression
Exercise: write a script, all files backed up daily 02:20 / etc directory, the name of today's date; and save the file as a compressed file;
crontab ---- 020 2 * * * bash /root/xxx.sh
vim xxx.sh
#!/bin/bash
#
tar cJvf /var/`date +%F`.xz /etc
b) Command History:
Role: use the View command between
About command history file: .bash_history - at root, the specialized storage command history, it will automatically write (history -a command can take advantage of the command stored in the memory in .bash_history) once at the time of shutdown
Variables on command history (environment variables): PATH is an environment variable
How --- Environment Variables View: env
--- view a more detailed environmental variable: set
history of common operations:
1, the exclamation mark + number (n!): View command history
2, exclamation + String (String!): A string of recent matches
3, exclamation + exclamation point (!): A command
4, + $ exclamation mark ($!): Same as the last parameter ESC + shortcut key on a command function.
Common options:
-a: Add
-d: delete
-c: Empty
#: # Display the most recent command line
c) command completion: tab key in the development environment \ t represents the four spaces
- prompt
- Autocomplete
d) directory completion: tab key
- prompt
- Autocomplete
Execution status e) command
In Linux, after the execution of each command will have two results:
Replace the contents of the command itself
Secondly, the command execution result status
Variable $? Variable is used to store the state of command execution
0 indicates a successful state (and python opposite)
1 represents a failure status to 255
f) command shortcuts
ctrl + l clear screen
ctrl + c End Process
ctrl + u to delete the character before the cursor
ctrl + k character after cursor is deleted
ctrl + a cursor jumps to the head
The cursor jumps to the end ctrl + e
ctrl + w a space-delimited files to delete
ctrl + r search again recently entered the command interface used (for input string)
g) alias alias
System boot sequence is read some special files
alias cdnet = "cd / etc / sysconfig / network-scripts /" can only be executed in the current shell
Global configuration file
/ Etc / profile define environment variables (for all users) the first to read the file
/ Etc / bashrc define local variables, local variables typically used to set (for all users)
Personal profiles (written in the user's home directory)
~ / .Bash_profile define environment variables (user specified)
~ / .Bashrc --- Alias definition of local variables (user specified)
sources / etc / profile or. / etc / profile file so that the entry into force
h) file wildcard globbing
Not a regular expression wildcard file
? Any single character
* Any character of any length
[] Any one character in the specified range
Any one character ^ [^] outside the specified range [^ 0-9A-Za-z]
Specify character classes: When calling in to add a []
[: Alnum:] letters + numbers
[: Alpha:] letter
[: Upper:] uppercase letters
[: Lower:] lowercase
[: Digit:] Digital
[: Punct:] special characters
[: Space:] space ^ [[: space:]] * $ spacebar have blank lines